As they're not releasing the rules in advance, it poses a game design challenge of what a zero-gravity sport might really be like. The criterion that the plane's flight only gives 30 seconds or so of 0-G at a time is an interesting sporting constraint, though I wonder whether they're missing a trick by not likewise making use of the zero-to-one G and more-than-one G conditions that are also engendered at different angles in the rotation. The casting call implies a seven-a-side game, even though the working drawings suggest three players going down the plane facing three players coming up it. Perhaps the two teams have specialist defensive and offensive units of three players each, but that seems unnecessarily labour-intensive to me.
My gut feeling is that they may be more restricted by the essential shape and size of an aeroplane cockpit than they suspect. The best-case assumption under current technology is that the game could take place in a Boeing 727, which is what Wikipedia reckon the Zero-Gravity Corporation use, which might possibly give a playing field 80-90 feet long, 11 feet wide and possibly 8-9 feet tall. (Probably less tall than that - see the pictures.) Trying to have a ball game in there is like the metaphorical knife fight in a phone booth. There's also Newton's First Law coming into play; there's going to be a lot of floating around unless there are useful things to push off. (Probably the other players and the walls, but potentially what else?) Quidditch would be a particularly bad choice, the fact that it's not inherently that good a game notwithstanding.
When you say zero-gravity, you think of people floating around, probably fairly slowly in order to maintain some degree of control. That's the preconception we need to play with in order to blow people's minds - we need people moving around quickly, we need people being just a bit out of control, we need people doing things they couldn't do in 2-D and mastering their flight. Perhaps little jet-packs might be a real option if we're relying them only for thrust rather than height? Perhaps there could be something lower-power but conceptually similar, like moderate-power aerosols?
Accordingly, I'd be tempted to suggested that Red Dwarf had it right with their throwaway reference to Zero Gravity Kick Boxing; I reckon there's no room for a ball game on an aircraft. Other popular sporting elementary concepts include combat sports, accuracy (targeting) sports and essential raw athletic contests. Space animal sports wouldn't fly (no pun intended) in this day and age - no space bull-riding. Artistic impression entertainment competitions: inevitable, but not with my name on them, and I can't see how they could be more fun than skysurfing already is. Mind sports wouldn't gain much from being played in space, though I'm sure there's an interesting 3-D game of Icehouse to be played somehow.
My first suggestion is a combat sport. It's a push of war (by analogy to tug of war) in zero-gravity. We would glove and pad everyone up, then have a full-contact sport where the aim is not to incapacitate your opponent but to push your opponent back. If you and your opponent both end up behind the opponent's goal line, you win and they lose. If a thirty-second chunk of low-gravity time expires and you're both between the goal lines, you just carry on from where you were in the next one; it's far more natural than boxing's artificial round structure. I suggest giving people one good push off the wall of their choice just before gravity hits zero, hoping to come off with greater momentum in the ensuing mid-air collision, then push your opponent back through whatever further contact you can orchestrate after that.
The clever bit is that we tie players to each other with loose-ish bungee cord which adds more forces to the system. This would bring players back together if they're floating too far apart from each other; pulling the other player towards you then also becomes possible. We would also draw a neutral point half-way down the cable and monitor it to determine whether the players really are moving one way or the other and whether the goal line has definitively been crossed or not.
I also wonder whether one-on-one is exciting enough, or whether we would have (say) two-player teams, each player attached to the three others. (I'm thinking more of a square-with-diagonal-lines-drawn arrangement here, not least because we can put the progress marker at the centre of the cross, rather than the pure but potentially slightly indeterminate tetrahedron.) It would be harder to commentate on but increase the chance of something really cool-looking happening; people flying off skew to each other isn't much fun - every missed opportunity for the action to take place wastes lots of money. Two-on-ones would be part of the game, though by necessity would happen only temporarily.
Would that work? I have a gut feeling there would be inherent uphill/downhill advantage parity issues, but these could be resolved through frequent changing of ends, maintaining the concept of distance won in previous attacks - if you've driven them a metre back, you should start with a metre advantage even if you're both heading the other way around. Are there any other obvious bugs and can they be fixed?
Unrelatedly, I don't think much of the Space Champions' business model of episodic PPV - though given how many porn sites maintain long-term subscriptions among their members, there must be something to it. It does desperately smack of "we can't get a TV deal for this", though. Time to tap the funds for kooky sport entertainment projects that are Red Bull and the Golden Palace Casino - everybody else is probably too sensible to touch it. (Perhaps one of the space tourism companies might want to get into the parabolic flights industry as a lower-priced alternative and run this as a loss leader for publicity?)
Lastly, any nominations for potential athletes and/or hosts for such an enterprise? I suggest that the athlete / model / contemporary philosopher Melanie Chisholm doesn't have much on her plate at the moment; surely it would be hard to beat the irresistible title Sporty Spice's Sport In Space...